Excise getindex adjoint

src/deprecated.jl

@@ -65,3 +65,9 @@ macro nograd(ex)
   end
   return blk
 end
+
+# Internal function used by some downstream packages.
+# Removing this completely would require some tricky registry changes,
+# but leaving it as a vestigial function is much easier.
+# See https://github.com/FluxML/Zygote.jl/pull/1328 for more context.
+function ∇getindex end

src/lib/array.jl

@@ -41,24 +41,6 @@ end
 @adjoint (::Type{T})(sz) where {T<:Zeros} = T(sz), Δ->(nothing,)
 @adjoint (::Type{T})(sz) where {T<:Ones} = T(sz), Δ->(nothing,)
 
-@adjoint getindex(x::AbstractArray, inds...) = x[inds...], ∇getindex(x, inds)
-
-@adjoint view(x::AbstractArray, inds...) = view(x, inds...), ∇getindex(x, inds)
-
-∇getindex(x::AbstractArray{T,N}, inds) where {T,N} = dy -> begin
-  if inds isa NTuple{N,Int} && T <: Number
-    dx = OneElement(dy, inds, axes(x))
-  elseif inds isa NTuple{<:Any, Integer}
-    dx = _zero(x, typeof(dy))
-    dx[inds...] = dy
-  else
-    dx = _zero(x, eltype(dy))
-    dxv = view(dx, inds...)
-    dxv .= accum.(dxv, _droplike(dy, dxv))
-  end
-  return (_project(x, dx), map(_->nothing, inds)...)
-end
-
 """
     OneElement(val, ind, axes) <: AbstractArray
 

test/gradcheck.jl

@@ -174,11 +174,11 @@ end
 
   # Ensure that nothings work with numeric types.
   _, back = Zygote.pullback(getindex, randn(4), [1])
-  @test back([nothing]) == (zeros(4), nothing)
+  @test back([nothing]) == nothing
 
   # Ensure that nothings work with non-numeric types.
   _, back = Zygote.pullback(getindex, [randn(2) for _ in 1:3], [1])
-  @test back([nothing]) == (nothing, nothing)
+  @test back([nothing]) == nothing
 end
 
 @testset "view" begin

test/utils.jl

@@ -2,14 +2,8 @@ using ForwardDiff
 using Zygote: hessian_dual, hessian_reverse
 
 @testset "hessian: $hess" for hess in [hessian_dual, hessian_reverse]
-
-  if hess == hessian_dual
-    @test hess(x -> x[1]*x[2], randn(2)) ≈ [0 1; 1 0]
-    @test hess(((x,y),) -> x*y, randn(2)) ≈ [0 1; 1 0]  # original docstring version
-  else
-    @test_broken hess(x -> x[1]*x[2], randn(2)) ≈ [0 1; 1 0]  # can't differentiate ∇getindex
-    @test_broken hess(((x,y),) -> x*y, randn(2)) ≈ [0 1; 1 0]
-  end
+  @test hess(x -> x[1]*x[2], randn(2)) ≈ [0 1; 1 0]
+  @test hess(((x,y),) -> x*y, randn(2)) ≈ [0 1; 1 0]  # original docstring version
   @test hess(x -> sum(x.^3), [1 2; 3 4]) ≈ Diagonal([6, 18, 12, 24])
   @test hess(sin, pi/2) ≈ -1